There are previously known safety interlocking systems for protecting electrical equipment users and technicians against hazards, such as electrical shock, burns, radiation, and improper operating modes.
For example, it is well known to enclose a hazardous apparatus in a protective cage having an access door or panel, the removal of which actuates a safety interlock switch. Such a safety interlock switch typically removes primary power from the electrical equipment and must, therefore, be rated to carry primary currents and voltages.
In another example, some electrical equipment include a module that is removable for servicing or replacement. Often the removable module is secured behind or attached to an access panel. Typically, such removable modules are secured within the electrical equipment by mechanical fasteners and have separate electrical interconnections, safety interlock switches, and related wiring harnesses.
Portable image projectors present an interesting mix of requirements and hazards. Many such projectors employ a metal-halide or mercury vapor arc lamp that operates at a very high temperature, requires a high voltage pulse to ignite the are, must be readily replaceable, must be compact and lightweight, and must be packaged to protect users and the projector from heat, high voltage, and improper operating modes, such as operation of equipment at excessive temperatures, and high-voltage pulse generation during arc lamp replacement.
Portable image projectors are generally referred to as being “ultra-portable” if they are small enough and light enough to be carried by one hand. However, in order to safely manage the above-described arc lamp hazards, prior art safety interlock apparatus have generally been relatively heavy and bulky, rendering them undesirable for use in ultra-portable projectors.
One such conventional prior art safety interlock design is shown in FIG. 1. As indicated, a DC power supply 1A receives high voltage alternating current (“AC”) line power from an electrical outlet along line 2A and provides positive direct current (“DC”) voltage to a lamp ballast power supply 3A, which generates a ballasted voltage for lamp 5A. A safety interlock switch 7A is placed along AC line 2A upstream of the DC power supply. To shut down the projector for lamp removal or the like, switch 7A is automatically actuated by opening a lamp access panel to interrupt the high voltage line current along line 2A. Interruption of the line power eliminates power to the DC power supply 1A, ballast power supply 3A, and lamp 5A, thereby rendering the projector safe for lamp removal. While this prior art approach is effective, interruption of the relatively high voltage AC line power requires a relatively large, expensive safety interlock switch 7A. Such high voltage switch needs to be well insulated and have substantial contact spacing requirements (e.g., 3 mm) in order to prevent electrical arcing, both of which tend to increase the size, weight and cost of the switch 7A.
What is needed, therefore, is a compact, lightweight, inexpensive and safe safety interlock system that is suitable for use in portable and ultra-portable image projectors.